1. Field of the Invention
The invention relates to a pressure sensor and more particularly to a pressure sensor with encapsulated circuitry.
2. Brief Description of Related Art
Absolute-pressure and relative-pressure sensors, for example, are used in pressure measuring technology. In the case of absolute pressure sensors, a pressure to be measured is detected in absolute terms, that is to say as a pressure difference with respect to a vacuum. A relative pressure sensor picks up a pressure to be measured in the form of a pressure difference with respect to a reference pressure. The reference pressure is an ambient pressure which prevails where the sensor is located. In most applications, this is the atmospheric pressure at the location of use.
Pressure sensors are used in a multiplicity of branches of industry, for example in chemistry and in the food industry. Frequently to be found in these industries are large installations in which pressures are to be measured at several points for the purpose of detecting, controlling, regulating and/or automating a process running in the installation. Use is made in this case of a multiplicity of pressure sensor, for example with different measuring ranges.
It is therefore advantageous both for the user on site, and for the manufacturer of the pressure sensors-for reasons of storage, maintenance and practicability-to design pressure sensors as a modular assembly which can then, if required, be provided on site with, for example, a meter housing having an electronic system tailored to the application, or with a process connection suitable for the measuring place.
Pressure sensors usually have a measuring cell, a measuring cell mount and an electronic sensor system connected to the measuring cell. In the case of modular. pressure sensors, the electronic sensor system must be accessible so that it can be connected, for example, to a meter electronic system or a supply and/or signal evaluation unit. However, it is precisely the electronic sensor system and the electric connections thereof which are particularly sensitive to moisture and to mechanical loads.
It is an object of the invention to provide a pressure sensor having a measuring cell, a measuring cell mount and an electronic sensor system connected to the measuring cell, in the case of which the electronic sensor system and its electric connections are protected against moisture and mechanical loads.
For this purpose, the invention comprises a pressure sensor having
a measuring cell,
a measuring cell mount, and
an electronic sensor system connected to the measuring cell,
in which the electronic sensor system is encapsulated in a protective cushion, and
in which the protective cushion is surrounded by an encapsulation.
In accordance with a development of the invention, a seal is injected in a gap existing in the radial direction between the measuring cell and the measuring cell mount.
In accordance with a further development, because of the dimensions of the measuring cell, the injected seal and the measuring cell mount a thermal expansion of the measuring cell and injected seal in the radial direction is equal to a thermal expansion of the measuring cell mount in the radial direction.
In accordance with a preferred embodiment, the injected seal consists of a silicone or of polyurethane.
In accordance with a preferred embodiment, the protective cushion is a foam plastic.
In accordance with a further preferred embodiment, the foam plastic has open and closed cells.
In accordance with a further preferred embodiment, the encapsulation is a polyurethane.
In accordance with a development of the invention, the pressure sensor has a metallic cover which extends between the encapsulation and the protective cushion.